Permo-Carboniferous volcanism in late Variscan continental basins of the Bohemian Massif (Czech Republic): geochemical characteristic
Introduction
Late Paleozoic basins of the Bohemian Massif occur in the Rhenohercynian, Saxothuringian and Moldanubian orogenic zones (Fig. 1). The lower part of the sedimentary sequence was deposited in marine or paralic environments (Lower Carboniferous), whereas its upper part consists of continental sediments (Upper Carboniferous and Lower Permian). Besides surface outcrops, the sediments with intercalated volcanics have been documented by thousands of boreholes and provide good constraints on the Westphalian and Stephanian stratigraphy. In addition, Carboniferous rocks are also known from underground mines.
The Bohemian Massif has a unique position within central Europe as the largest exposure of the Variscan Orogen. During the last years, several attempts have been made to characterize the late- to post-collisional volcanic activity and its role in the late stages of the Variscan Orogeny (W. Franke, 1989; D. Franke, 1995). The Variscan Orogeny, culminating at about 325 Ma, was accompanied by the emplacement of a range of subduction- and extension-related magmas (360 and 260 Ma — Lorenz and Nicholls, 1984; Downes and Duthou, 1988; Wilson and Downes, 1991). The mantle beneath the western and central Europe was metasomatized as a consequence of prior plate subduction during the Variscan Orogeny and especially during the late phases of the Late Paleozoic extension (Wilson and Downes, 1991; Wilson, 1993).
In the late Carboniferous, the Bohemian Massif became dissected by a conjugate system of wrench faults inducing formation of continental basins with volcano-sedimentary sequences that are often coal bearing. The Variscan collision in central Europe was followed by periods of magmatic activity both within the orogen and on its foreland. Compositional differences between the volcanic rocks were controlled by magmatic sources reflecting different tectonic settings and mantle heterogeneity. Crustal thickening and southward-increasing depth of origin of mafic magmas in the North German Basin may reflect the presence of a pre-existing subduction-influenced basaltic magma source (Benek et al., 1996).
Subalkaline, transitional subalkaline–alkaline and more rarely alkaline volcanism is characteristic for the Variscan foreland basin (N Germany), and continental intermontane basins (Germany, Czech Republic, Poland) of the Variscan Orogen. During the Namurian–Westphalian, intermontane basins started to form parallel to the Variscan Orogen (Ziegler, 1990); Mattern (2001) designated these “Basin Family One”. The late Variscan intermontane basins of central Europe are aligned along pre-existing structural discontinuities and tectonic lineaments of the basement (strike directions E–W, NE–SW and/or NW–SE). The Variscan Orogen was subjected to the Late Paleozoic gravity collapse associated with basin formation parallel to the Variscan structural plan (Ménard and Molnar, 1988). The broad zone of the basins implies, together with intensive volcanism, a substantial tension and thinning of crust (Benek et al., 1996). The origin of the Permo-Carboniferous volcanic activity in the Bohemian Massif can be linked with the Variscan orogenic collapse. Initial Variscan (325–290 Ma) collisional shortening and uplift was followed at ca. 290 Ma by extension. This is documented by the widespread volcanic activity and thinning of the Permian crust (Scholle et al., 1995). However, Jindřich (1971) related the Permo-Carboniferous volcanism with the (half)-graben structures along Precambrian lineaments and/or strike-slip faults caused by the taphrogenic movements induced by updoming of the Bohemian Massif during the Late Paleozoic and continuing up to the Tertiary.
Nevertheless, the integrated studies on the Permo-Carboniferous volcanics of central Europe that consider both their structural position and geochemical (isotopic) signatures come from the last decade only (Seckendorff, 1990; Hoth et al., 1993; Korich, 1989, Korich, 1992; Benek, 1991, Benek, 1995; Benek et al., 1996; Kölbl-Ebert, 1995; Dziedzic, 1996a, Dziedzic, 1996b; Arz, 1996; Seckendorff et al., 2004; Awdankiewicz, 1999a, Awdankiewicz, 1999b; Schmidberger and Hegner, 1999).
Section snippets
Distribution of the Permo-Carboniferous volcanism in the Late Paleozoic basins of the Bohemian Massif
Products of intensive volcanic activity associated with the Variscan Orogeny are abundant in the sedimentary fill of the Late Paleozoic basins of the Bohemian Massif. Accumulations of largely synchronous ancient volcanic sequences are present in Central Bohemian basins, Lusatian or Sudetic basins: Česká Kamenice Basin, Mnichovo Hradiště Basin, Krkonoše Piedmont Basin, Intra-Sudetic Basin, see Fig. 1. For stratigraphic correlation of basic units in individual basins see Fig. 2. Notable coeval
Methods of investigation
More than 60 rock samples were collected for new petrographic and geochemical investigations of the Permo-Carboniferous volcanics in late Variscan continental basins of the Bohemian Massif. The Variscan basins are mostly covered by sediments of the Czech Cretaceous Basin and the majority of rock samples (about 80%) are from cores of deep boreholes. Samples from the Central Bohemian, Česká Kamenice and Mnichovo Hradiště basins originate exclusively from boreholes. Surface samples are mostly from
Permo-Carboniferous volcanism in the Late Paleozoic basins of the Bohemian Massif: a review
Late Variscan magmatism in the Bohemian Massif culminated during late Carboniferous to Permian. Magmas of (basalt)/basaltic (trachy)andesite to dacite–trachyte–rhyolite composition extruded as both lava flows and pyroclastic deposits. In some places subvolcanic intrusions are present. From the stratigraphic record two main episodes of volcanism can be discerned in the Central Bohemian Basins and Sudetic Basins:
- 1.
Volcanic products of the first episode (late Namurian to Stephanian B) form a
Central Bohemian Basins and West Bohemian Basins
Volcanics in the Central Bohemian Basins and West Bohemian Basins are restricted to the Carboniferous and they are small in number. Their degree of alteration is very strong often ruling out any attempt of chemical classification. They are confined to 37 horizons (Pešek, 1994) with rhyolite prevailing in the majority of tuffs and tuffites. Felsic compositions are more abundant among effusives sporadically occurring in the Bolsovian and in the Westphalian D to Cantabrian deposits of the Central
Considerations about possible source areas of the Permo-Carboniferous volcanics in the Bohemian Massif
Localizing the source areas and centers of volcanic activity is problematic wherever intrusive feeder facies are missing/not preserved (Fig. 6). The source areas of the first volcanic episode (Duckmantian to Stephanian B) are documented by effusive and shallow intrusive bodies in central and NW Bohemia. Pešek (1994) and Pešek (1998) consider that there were further source areas in W and NE Bohemia that have not been preserved. By contrast, Mašek (1973) considered the Saxonian part of the Krušné
Trace elements and REE patterns
A review of the trace element distribution is presented in multi-element variation diagrams and REE patterns of the Permo-Carboniferous volcanics from individual basins of the Bohemian Massif (see Fig. 5a and b). The most complete trace element information comes from the Krkonoše Piedmont Basin and the Intra-Sudetic Basin (cf. Ulrych et al., 2004, Ulrych et al., 2003).
In the Krkonoše Piedmont Basin volcanics, normalized multi-element variation diagrams of both episodes show very similar
Sr–Nd isotope systematics
As for the trace elements, the most complete information is from the Krkonoše Piedmont Basin and the Intra-Sudetic Basin.
In the Krkonoše Piedmont Basin all mafic samples have low initial values between −2.7 and −6.0 and (87Sr/86Sr)i ratio (i — initial, ) of ca. 0.706–0.707. The felsic rocks reveal a substantial range of values (−0.9 to −5.1) and (87Sr/86Sr)i ratios (0.738–0.762). Epsilon values for rocks at their time of formation () were calculated using the expression:
Origin of the felsic rocks
The Intra-Sudetic Basin rhyolitic rocks show affinities with the andesites, having similar trends in the normalized multi-element variation diagrams and REE patterns. Several specific characteristics, e.g., strongly negative Ba, Nb, Sr, P, Ti, Eu anomalies in the felsic rocks suggest plagioclase, apatite and titanian magnetite fractionation.
The notorious composition gap between intermediate and acid rocks in the Permo-Carboniferous volcanic series of the Bohemian Massif is partly filled by
Discussion
New geochemical studies of the Permo-Carboniferous volcanic rocks of the Bohemian Massif (Central Bohemian Basins — Jelínek et al., 2003; Sudetic Basins — Ulrych et al., 2004, Ulrych et al., 2003) show that the parental magma of both episodes (Carboniferous and Permian) was likely derived from the mantle. The geochemical characteristics of the volcanic rock series suggest that the primary magma was underplated at the mantle–crust boundary and then evolved in crustal chambers by AFC processes.
Conclusions
Extensive Permo-Carboniferous volcanism of the intermontane continental basins of the Bohemian Massif represents the late Variscan activity in central Europe. Volcanics of the first episode (Carboniferous Series — Ulrych et al., 2003) started at the Duckmantian–Bolsovian boundary and continued intermittently until the Westphalian D to the Middle Stephanian producing felsic–mafic volcanics. During the second episode (Permian Series — Ulrych et al., 2003), after the hiatus between Stephanian B and C
Acknowledgements
Financial support for this research was provided by the by Grant Project A301 3903 of the Grant Agency of the Academy of Sciences of the Czech Republic and the Scientific Programme CEZ: Z3-013-912 of the Institute of Geology, AS CR. The authors are grateful to E. Hegner, University München for isotope data and help with their interpretation. V. Lorenz, University Würzburg, E. Pivec, Institute of Geology, Acad. Sci CR, Prague, and V. Prouza, Czech Geological Survey, Prague, are thanked for
References (75)
Geochemical criteria for redefined tectonic discrimination of orogenic andesites
Chem. Geol.
(1981)- et al.
Permo-Carboniferous magmatism of the Northeast German Basin
Tectonophysics
(1996) - et al.
Post-collisional transformation from calc-alkaline to alkaline volcanis during the Neogene in Oranie (Algeria)magmatic expression of a slab breakoff
Lithos
(2002) Geologic and geochemical reconnaissance of Isla San Estebanpost-subduction orogenic volcanism in the Gulf of California
J. Volcanol. Geoth. Res.
(1992)- et al.
Isotopic and trace element arguments for the lower-crustal origin of Hercynian granitoids and pre-Hercynian orthogneisses, Massif Central (France)
Chem. Geol.
(1988) Variscan plate tectonics in Central Europe—current ideas and open questions
Tectonophysics
(1989)- et al.
Post-collisional Variscan lamprophyres (Black Forest, Germany)Ar40/Ar39 phlogopite dating, Nb, Pb, Sr isotope, and trace element characteristics
Lithos
(1998) - et al.
Plate and intraplate processes of Hercynian Europe during the Late Palaeozoic
Tectonophysics
(1984) - et al.
The TiO2–K2O–P2O5 diagrama method of discriminating between oceanic and non-oceanic basalts
Earth Planet. Sci. Lett.
(1975) Magmatism and the geodynamics of basin formation
Sed. Geol.
(1993)
Magma mixing and contamination as mechanism to produce intermediate magmas in the late Variscan Saar-Nahe-Basin
Zbl. Geol. Plläont. Teil I 1994
Volcanism in a late Variscan intermontane throughthe Carboniferous and Permian volcanic rocks of the Intra-Sudetic Basin, SW Poland
Geol. Sud.
Volcanism in a late Variscan intermontane throughthe petrology and geochemistry of the Carboniferous and Permian volcanic rocks of the Intra-Sudetic Basin, SW Poland
Geol. Sud.
Aspects of volume calculation of paleovolcanic eruptive products—the example of the Teplice rhyolite (east Germany)
Z. Geol. Wiss.
Late Variscan calderas/volcano-tectonic depressions in Eastern Germany
Terra Nostra
The Teplice rhyolite (Krušné hory Mts., Czech Republic)—chemical evidence of a multiply exhausted stratified magma chamber
Věst Čes geol. Úst.
Chemical evolution of volcanic rocks in the Altenberg-Teplice Caldera (Eastern Krušné hory Mts., Czech Republic, Germany)
Geolines
Small-scale convection induced by passive riftingthe cause of uplift of rift shoulders
Earth Planet Sci. Lett.
Geochemical and tectonic transitions in the evolution of the Mogollon-Datail Volcanic Field, New Mexico, usa
Chem. Geol.
Permo-Carboniferous volcanics in Europe and northwest Africaa superplume exhaust valve in the centre Pangea?
J. Afr. Earth Sci.
Neogene magmatism and tectonics in the Carpatho-Pannonian region
Two-stage origin of the Hercynian volcanics in the Sudetes, SW Poland
N. Jb. Miner. Geol. Paläont Abh.
Genesis and evolution of Sudetic late Hercynian volcanic rocks inferred from trace element modelling
Geol. Sud.
Genesis and evolution of the Sudetic late Hercynian volcanic rocks inferred from the trace element modelling
Geol. Sud.
The Hercynian molasse and younger deposits of the Intra-Sudetic Depression, SW Poland
N. Jb. Miner. Geol. Paläont Abh.
The mineralogy and petrology of Tertiary-Recent orogenic volcanic rockswith special reference to the andesitic-basaltic compositional range, pp. 26–87
Melaphyres in structural boreholes of the profile line Mělnik-Ještěd
Sbor Geol. Věd Ř Geol.
Permokarbonische Vulkanite unter der Böhmischen Kreidetafel
Ber. Dtsch. Gesell geol. Wiss B Miner Lagerstättenforsch
Melaphyre rocks of northern margin of the Mnichovo Hradiště Depression
Sbor Severočes Mus přír Vědy
The North Variscan Foreland
Alkaline complexes from the Arabian Shield
J. Afr. Earth Sci.
Geochemistry and petrogenesis of a Cambrian ring complexan example of alkaline magmatism at Wadi Dib, Eastern Desert, Egypt
Chem. Erde
Review of Nd isotopic data and xenocrystic and detrital zircon ages from the pre-Variscan basement in the eastern Bohemian Massifspeculations on palinspastic reconstructions
Spec. Publ. Geol. Soc. Lond.
Cited by (42)
Petrogenesis of post-collisional Late Paleozoic volcanic rocks of the Bohemian Massif (Central Europe): Isotopic variations of the lithospheric mantle related to Variscan orogeny
2020, LithosCitation Excerpt :Post-collisional volcanism is well documented from many Cenozoic to Recent orogens (e.g., Aldanmaz et al., 2000; Coulon et al., 2002; Fedele et al., 2016; Miller et al., 1999; Perkins et al., 2018) and is associated with the Late Paleozoic Variscan orogeny (continent-continent collision) and is widespread in Central Europe, particularly in the Bohemian Massif. In this massif, the post-collisional volcanic rocks occur (Awdankiewicz, 1999, 2006; Awdankiewicz et al., 2013; Awdankiewicz and Kryza, 2012; Benek et al., 1996; Hoffmann et al., 2013; Ulrych et al., 2006) in a series of large Late Paleozoic volcano-sedimentary basins (Paulick and Breitkreuz, 2005) where they were emplaced in an extensional intracontinental regime. The study of these Late Paleozoic volcanic rocks of the Bohemian Massif can help to refine the understanding of the late stages of the Variscan orogeny, the variations in the composition of the continental lithospheric mantle (CLM) and the nature of igneous activities during that time.
Neoproterozoic to Cenozoic magmatism in the central part of the Bohemian Massif (Czech Republic): Isotopic tracking of the evolution of the mantle through the Variscan orogeny
2019, LithosCitation Excerpt :Unlike the other TBB and S-STB volcanic suites, the latest Carboniferous-Early Permian mafic rocks have negative ƐNd(t) values (Table 2; Figs. 6 and 7). The values are comparable to the data reported by Ulrych et al. (2002b, 2004, 2006) from the Late Paleozoic basins elsewhere in the Bohemian Massif. Their Nd model ages yield values of about 1050 to 1300 Ma (Fig. 8) suggesting the involvement of Precambrian material in the source of these rocks.